ECOLOGIA BALKANICA2019, Vol. 11, Issue 1 June 2019 pp. 191-204
Distribution, Characteristics and Ecological Role of ProtectiveForest Belts in Silistra Municipality, Northeastern Bulgaria
Kiril V. Vassilev1*, Assen I. Assenov2, Nikolay I. Velev1,Borislav G. Grigorov2, Bilyana B. Borissova2
1 - Bulgarian Academy of Sciences, Institute of Biodiversity and Ecosystem Research, Departmentof Plant and Fungal Diversity and Resources, G. Bonchev str. 23, 1113, Sofia, BULGARIA;
2 - Sofia University “St. Kliment Ohridski”, Faculty of Geology and Geography, Department “LandscapeEcology and Environmental Protection”, 15, Tzar Osvoboditel Blvd. 1504 Sofia, BULGARIA
Abstract. Protective forest belts are developed as a defense against dry winds and soil moisture lossand considered as natural capital nowadays. Silistra municipality’s protective forest belts wereinvestigated about their distribution, floristic composition, vegetation structure and syntaxomony.During 2018 field season 32 relevés were collected following the Braun-Blanquet approach. Dataabout diversity of invasive and melliferous plants were collected also. Vegetation types wereidentified by numerical classification using hierarchical agglomerative clustering (PC-ORD).Descriptive statistics about the cover of tree, shrub and herb layers as well as cover of invasive andmelliferous plants were graphically summarized in vertical box-and-whisker plots. The forest beltssyntaxonomical diversity is represented by 2 associations (Cotino coggygriae-Quercetum cerris, Bromosterilis-Robinietum) and Amorpha fruticosa-Morus alba plant community. Cotino coggygriae-Quercetumcerris has closed horizontal structure with dominants Quercus cerris and Cottinus coggygria in treeand shrub layers respectively. Bromo sterilis-Robinietum is characterized by poor speciescomposition and vegetation dominated by Robinia pseudoacacia and Fraxinus americana, whereasAmorpha fruticosa-Morus alba community has local distribution and represents a final stage ofvegetation degradation. Totally five alien species (Acer negundo, Amorpha fruticosa, Erigeron annuus,Fraxinus americana and Robinia pseudoacacia) and 26 melliferous plants were identified within theforest belts. The highest cover of invasive species and melliferous plants were found within Bromosterilis-Robinietum and Amorpha fruticosa-Morus alba. The main melliferous plant species wereRobinia pseudoacacia, Amorpha fruticosa, Morus alba and Prunus cerasifera. The investigated forest beltvegetation bears the characters of a long-standing anthropogenic impact. They have been subject tocutting, burning and pasturing during the last 50-60 years.
IntroductionProtective forest belts are of a particular
historical importance for shielding againstdry winds and for preserving soil moisture.The contemporary interpretation considers
them as natural capital, providingregulating, cultural and few direct materialecosystem/landscape goods and services,but significant indirect materialecosystem/landscape goods and services, as
Union of Scientists in Bulgaria – PlovdivUniversity of Plovdiv Publishing House
Distribution, Characteristics and Ecological Role of Protective Forest Belts in Silistra Municipality...
a product of the nearby agricultural areas(pollination of crops and other plants,purification of water and air, etc.).Geographically determined, the firstprotective forest belt emerged in theKingdom of Russia under the influence of aRussian forester, named Nestor KarlovichGenko (1839-1904). The continental climate,characterized by insufficient rainfall and theemergence of dry winds, leading to erosionand drying of the soil, is a prerequisite forthe creation of protective forest belts,particularly in this part of the world. Theseprocesses, along with the destruction of theEuropean forests in the period 1750-1850,provoked the need of the foundation anddevelopment of the forestry science (POPOVet al., 2017). During the period 1886-1903protective forest belts in Ulyanovska Oblasthave been established and today they are aprotected natural object. The total aerialcoverage of the forest belts “Genko stripes”in Samara Oblast is nearly 9 000 hectares andtheir total length is around 150 km, whiletheir width is 640 m.
As Genko was working on theplantation of the protective forest belts, thesame idea was adopted in the neighboringcountry of Romania, where BRAD (1850)created the first plantations as “sheltersagainst wind”. Romania had a leading rolein the creation of protective forest belts withits Barăgan plain for forest belts from 1906,which is more than 39 years younger thanthe plan of Roosevelt and 42 years youngerthan the plan of the Soviet Union fortransformation of nature, following BUCUR(2016). In 1936 the plantation of forest beltsin the villages of Karvuna (BalchikMunicipality) and Rogozino (DobrichMunicipality) started and two years laterplantations were finished. The work inKarvuna village continued in 1939 and 1940when according to the Treaty of Craiovathese lands were returned to Bulgaria,POPOV et al. (2017).
The October Revolution in 1917 ceazedplantations, but after World War I, specialmeasures for the creation of new forest belts
were applied in Romania. During this periodthe first plantations of protective forest beltsin the occupied Bulgarian SouthernDobrudzha have been established.
The end of World War II sawnationalization of lands in Bulgaria andRomania. State act (№ 236) was adopted inBulgaria in 1951, concerning thedevelopment of agriculture, water supplyand electrification in Dobrudzha and inparallel with this a plan-program for thecreation of protective forest belts was alsobrought to light. Soon after that anexpedition, studying forest belts inDobrudzha, was led and a book waspublished by STOYANOV & KITANOV (1955),where soil scientists, hydrologists, botanistsand zoologists made contributions also.
According to POPOV et al. (2017) thebulgarian government ordered the creationof nine protective forest belts, covering 21997 ha in total and with 800 km length (fig.1).The belts have 70-90 m in width andplantations were planted in 1951 –1958. Thetree species Quercus robur, Quercus petraea,Fraxinus excelsior, Robinia pseudoacacia,Gleditsia triacanthos, Juglans regia and Populusssp. were planted according to POPOV et al.(2017). As of 1980 the average height of thebelts was 5-15m and the stock are 389 000 m3.Forest belts are protecting agricultural areawith cells 500-600 m wide and 1200-2000 mlong. The prevailing winds in this territorycome from the north, so the main belts areoriented in east-west direction, having adistance of 500 m in-between. According toGEORGIEV (1960) the impact of the belts isdivided in an equal distance from them,multiplied by 25-30 height.
The protective effect of the forest beltscan be summarized in the following way: thewind effect has been reduced with 25-30%,air moisture deficit has been reduced by 15-20% and physical evaporation has beenreduced by 7-20%, according to VACHOVSKI& DIMITROV (2003). Snow cover started toaccumulate equally at the direction of thesnowfall within the belts, while soil moisturewas kept in the horizon between 100 and 200
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cm with an increase of 45-50%. Among theexisting protective forest belts in Bulgaria,the ones in Dobrudzha have the best status,according to POPOV et al. (2017).
Forest belts can be analyzed as linearelements in landscape structure that directlyinfluence ecological processes, followingFORMAN & BAUDRY (1984) and landscapefunctions, according to MARSHALL &MOONEN (2002). European history ofagriculture acknowledges constructive roleof linear elements in the formation andfunctioning of a wide variety of rurallandscapes, following ZIMMERMANN (2006).The understanding of landscape’s patterninteractions – arable fields (matrix) andadjacent green corridors (linear elements),are essential for biodiversity complexityexplanation, according to MEYER et al. (2012).Linear landscape elements are a valuableindicator for the biological diversity in agro-landscapes, following BILLETER et al. (2008).
Landscape Ecology considers linearelements as sources of important ecosystemservices, according to VAN DER ZANDEN et al.(2013) and stimulates multi-functionallandscape utilization. Depending on thegeographical circumstances and landmanagement priorities the primary role ofphysical fluxes regulation (erosion and windreduction, increased water infiltration,enhanced carbon sequestration, pollutioncontrol) can be expand with the functions ofbiological corridors (or, in particular, nectarcorridors), or even cultural services(recreation, aesthetics). For this reasonsubstantial for land management is linearelements’ investigation and modelling(number, mean size, length, mean shape) inthe landscape scale, according to MÜCHER etal. (2009).
The aims of the study are: (1) researchof the published Bulgarian and foreignliterature related to development of forestbelts; (2) investigation of distribution,floristic composition and vegetationstructure of protective forest belts in Silistramunicipality; (3) mapping of forest belts onthe territory of municipality; (4) analysis of
the anthropogenic influence and distributionof alien and melliferous plants of studiedforest belts.
Materials and Methods
Study areaProtective forest belts in the
municipality of Silistra were the object of thecurrent investigation and they were built-update back from 1951-1958. Its area covers51589.1 hа of which 38754.4 hа areagricultural territories, 6827.3 hа forest areas,3622.6 hа urbanized territories, 1809.0 hаwater areas, 51.0 hа quarries and transportinfrastructure takes up to 524.8 hа. SilistraMunicipality comprises around 18% of theterritory of the whole province (Silistra).There are also eighteen villages and onetown - Silistra, which is the center of theprovince and the municipality (Municipaldevelopment plan 2014-2020). The plainrelief reaches up to 200 m a.s.l. The fertilelowland of Baltata, located near Aidemirvillage, is also situated here and thesouthwestern part of the plain is taken bySrebarna Lake. “Srebarna Nature Reserve”represents the core zone of the “SrebarnaBiosphere Park“, created in 2017, followingthe Seville Strategy (1995) after VLADIMIROV
(2011). The biosphere park consists of a corezone, a buffer zone and a transition zone andthe whole area of Silistra Municipality islocated within its boundaries.
From biogeographic point of view, themunicipality is a part of the biogeographicprovince of Lower Danube River and theregion of Dobrudzha and belongs to thebiome of Aestiduriherbosa, according toASSENOV (2006).
Data collection and statistical analysisDuring 2018 field season 32 reléves
(vegetation plots) were collected, followingthe approach by BRAUN-BLANQUET (1965).The plot size was 400 m2, as recommendedfor forest communities by CHYTRÝ &OTÝPKOVÁ (2003). For every reléve allspecies were recorded as well as information
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about altitude, aspect, slope, total vegetationcover, cover of tree, shrub, herb andcryptogam layers, soil depth, bedrock type,locality, GPS coordinates.
All reléves were stored in the BalkanVegetation Database (VASSILEV et al., 2016).The numerical classification was performedby PC-ORD, following MCCUNE & MEFFORD
(1999) and JUICE 7.0 by TICHÝ (2002)software packages using Bray-Curtisdistance and flexible beta algorithm onsquare-root transformed and three cut levels(0, 5, and 25) were used.The diagnostic species were determined bycalculating the Phi-coefficient by CHYTRÝ etal. (2002). Two values were given for eachspecies in the synoptic table: “Fidelity”expressed by the Phi-coefficient and“Constancy” expressed in percentage. Allclusters were standardized to equal size,following CHYTRÝ et al. (2006). Only thestatistically significant Phi-coefficient valuesevaluated by Fisher’s exact test (*P<0.05)were considered.
Descriptive statistics about the cover oftree, shrub, herb, invasive and melliferousplants layers were graphically summarizedin vertical notched box-and-whisker plots.Individual points in-line with the whiskerswere used for plotting the outliers (°).TheShapiro-Wilk test was used for testing thenormality of the data. Since only the data setof the invasive species cover met theassumption of normal distribution, the t-testwas applied for comparing the groups ofsamples. In all other cases the Mann–Whitney U nonparametric test was applied.Statistical computing and box-plot datavisualization were performed by R softwareenvironment (R Core Team, 2019).
The nomenclature of vascular plantsfollowed DELIPAVLOV & CHESHMEDZHIEV
(2003). The list of alien species was createdafter merging data from DELIPAVLOV &CHESHMEDZHIEV (2003), ASSYOV & PETROVA(2012), PETROVA & VLADIMIROV (2012, 2018),PETROVA et al. (2012), STOYANOV et al. (2014),TUTIN et al. (1964-1980). It includes totally450 species. Also a generalized list of
melliferous plants from Bulgarian flora wascreated, which contains 493 vascular plants(STOYANOFF, 1933; PETKOV, 1979; BRATANOV,1987; BIZHEV, 2003; TASHEV & PANCHEVA,2009; TASHEV et al., 2015).
During the field work we also mappedforest belts and measured their width in twoedges and central part. Later in ArcMap 10they were mapped as linear polygons.
Results and Discussion
Forest belt structure and distributionThe measurements made show that the
area of the protective forest belts and theexisting forests in the municipality of Silistrarepresents 4.7% of the total area (1.4% forprotection forest belts and 3.3% for forests,Fig. 2).
The forest belts are widely distributedon the territory of Silistra municipality and atotal number of 144 forest belts wereidentified (Fig. 2). Their length variesbetween 107.5 m and 7610.7 m (average1949.6 m), whereas the width is between 6 mand 146 m (average 43.4 m). They representlinear polygons around other polygons inthe landscape pattern (arable fields,woodlands, pastures, scrubland vegetation,etc.).
Vegetation types of forest beltsForest belts in Silistra municipality
comprises 3 vegetation types (Fig. 3; Table 1)– ass. Cotino coggygriae-Quercetum cerrisRousakova & Tzonev 2003 , ass. Bromosterilis-Robinietum (Poćs 1954) Soó 1964 andAmorpha fruticosa-Morus alba community.
Ass. Cotino coggygriae-Quercetum cerrisROUSAKOVA & TZONEV (2003). Thisvegetation represents widely distributedforest belt type, e.g. 23 studied forest belts(Fig 3, clusters 1-23; Table 1). It is found onflat to slightly-inclined terrains. Soils aremoderately-deep to deep. The length andwidth of forest belts is between 275.7 m and7082.2 m and 29.8 m and 76 m, respectively.
It has closed horizontal structure withvegetation cover 95-100%. Tree layer has cover
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between 50 and 95% and Quercus cerris is thedominant species. Other species with highercover and abundance are Fraxinus americanaand in some stands Robinia pseudoacacia. Shrublayer is well developed with cover between 10and 95% (average 77%), where Cotinuscoggygria is a dominant species andsubdominant is Ligustrum vulgare. In stands,where tree layer has been cut during last 10-15years cover of shrubs vegetation has beenincreased and are also found Rosa canina,Prunus spinosa and Rubus caesius. Herb layerhas cover between 1 and 100% (average 31%)and species with higher cover and abundanceare Geum urbanum and Myrroides nodosa (Fig. 4).
Cotino coggygriae-Quercetum cerris wasestablished from central Danubian plainaccording to ROUSAKOVA & TZONEV (2003)and floristically and ecologically is similar tophytocoenosis from Silistra municipality.The high cover of Cotinus coggygrya is aresult of successional changes incommunities, where it has faster growingthan other shrub species (such as Crataegusmonogyna, Prunus spinosa) and is a result ofhuman influence of the givenphytocoenoses. Similar trend has been alsoobserved from ROUSAKOVA & TZONEV
(2003).Аss. Bromo sterilis-Robinietum (Poćs
1954) Soó 1964. This association includesplanted Robinia pseudoacacia plantations (Fig.3, clusters 24-30; Table 1). Seven researchedforest belts were classified to this vegetationtype. The width and length of forest belts isbetween 32.2 m and 57.2 m and 130.2 m and3862.2 m, respectively.
It is characterized by poor speciescomposition. Dominant species is Robiniapseudoacacia (25-95%) and subdominant isFraxinus americana (10-55%). Tree layer iswell-developed and has total cover between70-100%. In two stands Robinia pseudoacaciarepresent a high shrub formed shrubbyvegetation. The shrub layer is formed byyoung trees of above mentioned species aswell as Crataegus monogyna, Rosa canina,Prunus cerasifera. Herb layer has coverbetween 30 and 100% and is well developed
mainly by Bromus sterilis, Galium aparine andGeum urbanum (Fig. 4).
Amorpha fruticosa-Morus alba plantcommunity.
Communitiy of Amorpha fruticosa andMorus alba is locally distributed and wasidentify in only one forest belt (Fig. 3; Table1). It characterize the final stage ofdegradation of vegetation, which has beenfired and cut in the past. Total vegetationcover is 95%. Tree layer is formed by Morusalba (50%) and Pyrus pyraster (15%). Theshrub layer is dominated by Amorphafruticosa (70%). Undergrowth is formedmainly by Bromus sterillis and Geumurbanum.
Distribution and species richness of alienand melliferous plants of forest belts
Forest belts floristic diversity isrepresented by 80 vascular plants. Forest beltsare reservoir of alien and melliferous plants inDanubian plain. Totally five alien species(Acer negundo, Amorpha fruticosa, Erigeronannuus, Fraxinus americana and Robiniapseudoacacia) were found in the speciescomposition. Their coverage and distributionin the studied region depended on thevegetation type. Robinia pseudoacacia andAmorpha fruticosa have lower coverage incommunities of Cotino coggygriae-Quercetumcerris association. Amorpha fruticosa coversbetween 0.5 and 10% as a shrub or juvenilespecies and was registered only in 4 relevés,whereas Robinia pseudoacacia was found in 5relevés and has cover between 3 and 40% as alow-tree, shrub and juvenile plant. Thecoverage of invasive species is increasing incommunities of Bromo sterilis-Robinietum andAmorpha fruticosa-Morus alba. The highercoverage of alien species in ass. Bromo sterilis-Robinietum is a result of dominance of Robiniapseudoacacia (coverage between 15 and 95%),whereas in Amorpha fruticosa-Morus albacommunities Amorpha fruticosa is a dominantspecies (coverage 70%). Fraxinus americana is aconstant species in tree, shrub and herb (asjuvenile plant) layers in Cotino coggygriae-Quercetum cerris and Bromo sterilis-Robinietumassociations.
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Diversity of melliferous plants in forestbelts is significantly higher and includes 26species (e.g. Acer campestre, A. negundo, A.tataricum, Agrimonia eupatoria, Amorpha fruticosa,Berteroa incana, Buglossoides purpurocaerulea,Cirsium arvense, Clematis vitalba, Consolidaregalis, Cornus mas, Crataegus monogyna,Eryngium campestre, Fraxinus ornus, Glechomahederacea, Juglans regia, Lamium purpureum,Ligustrum vulgare, Morus alba, Prunus cerasifera,Pyrus pyraster, Robinia pseudoacacia, Sambucusnigra, Syringa vulgaris, Tilia platyphyllos, Viciavaria). The number of melliferous plants invegetation plots of three types of forest belts issimilar (between two and six), but theircoverage is different. Communities of Cotinocoggygriae-Quercetum cerris association haveaverage cover of melliferous plants 40%,whereas it is increasing to 72% for communitiesof Bromo sterilis-Robinietum association. This isdetermined by higher cover of Robiniapseudoacacia, which is a widespread melliferousplant in the region. In species composition ofAmorpha fruticosa-Morus alba community coverof melliferous plants is 95%, which is
determined by dominance of Amorpha fruticosa,Morus alba and Prunus cerasifera.
dating back to 1950-1960’s of the twentiethcentury. Species used for planting have beenQuercus cerris, Robinia pseudoacacia, Gleditsiatriacanthos, Fraxinus americana. The threeidentified vegetation types represent differentsuccessional stages as a result of continuinganthropogenic pressure. Communities of Cotinocoggygriae-Quercetum cerris association areformed during last 50 years and their speciescomposition and structure are very close to itssemi-natural phytocoenoses in Danubian plain.Phytocoenoses of Bromo sterilis-Robinietumassociation represent anthropogenic vegetation,which has replaced communities of Cotinocoggygriae-Quercetum cerris as a result of cuttingof woody vegetation followed by successionalprocesses. Here Robinia pseudoacacia is adominant species. Its communities have semi-open horizontal structure, which leads to highercover of herb species (Fig. 4).
Fig. 1. Protective forest belts in Dobrudzha (POPOV et al., 2017, processed after VACHOVSKI &DIMITROV, 2003; DOBREV & PESHEV, 1957; ZAHARIEV, 1959).
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Fig. 2. Map of Silistra Municipality highlighting forest protection belts, mapped vegetationplots and existing forest vegetation outside the belts.
Fig.3. Vegetation types of forest belts in Silistra Municipality.
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Photo 1. Phytocoenosis of association Cotino coggygriae-Quercetum cerris.
Photo 2. Phytocoenosis of Amorpha fruticosa-Morus alba community.
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Fig. 4. Overall patterns about cover of tree, shrub, herb, invasive and melliferous plantslayers visualised by notched box-and-whisker plots. Cover is presented in percentages.Statistically significant differences at *P < 0.05 between groups observed for the cover of
herb, invasive and melliferous plants only.
Coverage and diversity of woody species,which formed tree and shrub layers, ishigher in communities of Cotino coggygriae-Quercetum cerris association, which formclosed horizontal structure and significantdegree of shading. Finally, communities ofAmorpha fruticosa and Morus alba representfinal stage of degradation of vegetation.Morus alba, which traditionally has beenused as fruit tree during centuries, has beenplanted closely to villages, around arablefields.
In the period of their existence the forestbelts have been subject to increasedanthropogenic pressure such as cutting,burning, some forest belts are used aspastures during summer months, etc. Thesmall width of belts and long-termanthropogenic pressure around them haschanged their species composition and leadto increasing of alien species in theircommunity.
The field research of the forest belts inthe municipality of Silistra shows that the
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most significant changes were made insubsection b of section 607, classified as object№ 1814, state/municipal property, contractedby Silistra State Forestry under contract No.5/16.01.2018 for logging with Les green Ltd.As a result of the implementation of thiscontract, logging was carried out in theappointed section and the rest of the sectionwas cut 15 years ago and turned into a bush-like outgrowth of a belt. Given the small shareof the forest cover of the municipality ofSilistra (4.7%), it is hardly environmentallyappropriate to carry out logging from theforest protection belts, especially sinceaccording to the law on forests, bare cuttingsare forbidden. In the studied forest belts inindividual places were recorded traces offelling of individual trees, which can beclassified as poaching. In both cases, therewere no traces of tree species disease.Subsection 607 b is located at thesouthernmost and relatively high in altitudepart of the municipality. In the forestprotection belt itself, a wooden observationpost, probably for the identification of fires,has been constructed after the cutting of thetall trees due to the lack of visibility beforethat. We can assume that in the highest part ofthe relief of the municipality located awayfrom the erosion bases of the Danube River,the protective belts serve to keep the snowfall,thus provide a reserve of soil moisture ratherthan to protect against wind erosion. Also,field studies have shown that in places, whereasphalted roads provide direct access to forestprotection belts, the border areas for
penetration through agricultural lands havebeen deeply plowed in order to prevent theaccess of cars and heavy vehicles.
ConclusionThe authors believe that the forest
protection belts condition in themunicipality of Silistra is very good and theyplay their role in maintaining the soilmoisture and protecting against water andwind erosion. Forest protection belts alsoplay the role of nectar corridors, which inthis area of small share of forest cover arevital for carrying out the pollinationecosystem service. Regardless theinvolvement of invasive species in the forestbelts, they do not pose an immediate threatthrough the continuous expansion of theirarea, because the agricultural areas on bothsides of the belts are being plowed everyyear and the herbicides used do not allowthe invasive species to spread.
By its nature, this study is innovativewith the attempt to establish thesyntaxonomic relation of the forestprotection belts and to show their role asnectar corridors in the country especially formunicipalities and regions with very smallshare of forest cover.
AcknowledgementsThe research has been conducted with
the support of the department of LandscapeEcology and Environmental Protection at theGeology and Geography Faculty of SofiaUniversity “St. Kliment Ohridski”.
Table 1. Synoptic table of forest belts vegetation types of Silistra municipality. The speciesare represented by two indicators: Fidelity measure, expressed by the Phi-coefficient (Chytrý &al. 2002) and Constancy, expressed in percentages. Original cover/abundance scale assessmentsused for Amorpha fruticosa-Morus alba plant community since it is presented by one reléve only.
Vegetation type Ass. Cotino coggygriae -Quercetum cerris
Ass. Bromo sterilis-Robinietum
Amorphafruticosa-
Morus albacommunity
Number of reléves 24 7 1Average species 14 16 14
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number per relevéFidelity / Constancy Phi C Phi CDiagnostic species of ass. Cotino coggygriae-Quercetum cerrisCotinus coggygria 86.7 96 --- 14 ---Quercus cerris 78 96 --- 29 ---Diagnostic species of ass. Bromo sterilis-RobinietumRobinia pseudoacacia --- 21 86.1 100 ---Bromus sterilis --- 33 37.8 100 2Diagnostic species of Amorpha fruticosa-Morus alba plant communityAmorpha fruticosa --- 17 --- 57 4Morus alba --- 0 --- 14 4Diagnostic species of cl. Quercetea pubescentis, ord. Quercetalia pubescenti-petreae &all. Quercion confertae Crataegus monogyna --- 100 --- 100 ---Euonymus verrucosus --- 33 --- 14 ---Brachypodium sylvaticum
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